Toothed belt

ABSTRACT

Toothed belt for use in contact with oil and comprising a body and a number of teeth extending from at least one surface of the body; the teeth are coated by a fabric; a resistant layer comprising a plastomer based on fluorine with the addition of elastomeric material, in which the plastomer is present in a larger quantity than the elastomeric material, is applied by adhesion onto the coating fabric. The elastomeric material forming the body of the belt is a copolymer obtained from a dienic monomer and a monomer containing nitrile groups, in which the nitrile groups are between 33% and 49%, preferably 39%, in weight with respect to the copolymer.

This application is a continuation of U.S. patent application Ser. No.10/590,224 filed Apr. 2, 2007 entitled “Toothed Belt” which is a 371filing of PCT/IT04/00081 filed Feb. 23, 2004, the disclosures of whichare incorporated herein by reference.

TECHNICAL FIELD

The present invention concerns a drive system comprising a toothed beltand, in particular, a toothed belt for use in an oil bath.

BACKGROUND ART

Toothed belts generally comprise a body made of elastomeric material, inwhich a number of longitudinal filiform resistant inserts, also calledcords, are embedded, and a number of teeth coated in a coating fabric.

Each belt component contributes to increasing performance in terms ofmechanical resistance, in order to reduce the risk of breakage of thebelt and increase the specific power that can be transmitted.

The belt coating fabric increases the resistance to abrasion andtherefore protects the work surface of the belt from wear due to rubbingbetween the sides and tops of the belt teeth and the sides and bottomsof the races of the pulley with which the belt interacts.

Furthermore the coating fabric reduces the friction coefficient on thework surface, reduces the deformability of the teeth and above allreinforces the roots of the teeth thus avoiding breakage.

The coating fabric used can consist of a single layer or, alternatively,can be a double layer in order to guarantee greater strength andrigidity. The fabric is normally treated with an adhesive, for exampleRFL (resorcinol and formaldehyde latex) to increase the adhesion betweenthe body and the fabric.

Currently many drive systems use gears or chains instead of toothedbelts. Both gears and chains are, however, complex systems to produce.Both chains and gears are noisier and operate exclusively with oil,furthermore during operation they are subject to greater elongation andtherefore replacement with a belt permits greater meshing precision.

In addition to these main disadvantages, both chains and gears are verycostly.

For these reasons it is expedient to replace chains and gears withtoothed belts without having to perform any other modification to thedrive system as a whole; in this case, therefore, the toothed belt wouldnecessarily have to operate in contact with oil or even partiallyimmersed in oil.

Numerous studies have already been carried out on toothed belts toascertain whether they are able to operate in direct contact with oil.For example, U.S. Pat. No. 4,099,422 describes a toothed belt designedto be used in an oil bath and comprising a body made of elastomericmaterial, preferably epichlorohydrin and a double layer of fabriccoating the teeth.

The patent application EP 0 549 401 describes a toothed belt comprisinga body consisting of a first layer in CSM or ACSM and a second layer onthe tooth side consisting of a matrix of HNBR coated with a fabrictreated with HNBR.

In contact with oil, in particular during meshing of the belt on thepulley, the elastomeric materials used to form the body of the belt aresubject to undesired expansion which causes a reduction in mechanicalcharacteristics, reduced adhesion and, due to dimensional variations,also less efficient meshing.

Furthermore none of the known toothed belts are particularly resistantto wear.

All the above problems therefore lead to easier breakage of the belt andtherefore a shorter average working life.

No toothed belt in use in contact with oil or partially immersed in oilis therefore able to resist the scheduled duration tests for use invehicle drive systems.

DISCLOSURE OF THE INVENTION

The scope of the present invention is therefore to obtain a toothed beltthat can be used in contact with oil or even partially immersed in oilwithout affecting the performance of the belt and maintaining thenecessary mechanical characteristics of adhesion, resistance to wear andmeshing precision.

According to the present invention said scope is achieved by a toothedbelt according to claim 1.

According to the present invention, a drive system is also suppliedaccording to claim 16.

BRIEF DESCRIPTION OF THE DRAWINGS

For a better understanding, the present invention is described also withreference to the attached figures, which show:

FIG. 1 is a perspective and partial view of a toothed belt according tothe present invention;

FIG. 2 is a diagram of a first timing control system using a firsttoothed belt according to the present invention;

FIG. 3 is a diagram of a second timing control system using a secondtoothed belt according to the present invention; and

FIG. 4 is a diagram of a third timing control system using a thirdtoothed belt according to the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

FIG. 1 illustrates as a whole a toothed belt 1. The belt 1 comprises abody 2 made of elastomeric material, in which a number of longitudinalfiliform resistant inserts 3 are embedded. The body 2 features a firstface provided with teeth 4 coated by a coating fabric 5 and a secondface or back 6 of the belt. Preferably the back 6 is also coated by afabric 7.

Even more preferably the fabric 5 which coats the teeth 4 is the same asthe fabric 7 that coats the back 6.

The body 2 comprises as main elastomer, or present in over 50% in weightwith respect to other elastomers used in the compound, a copolymerformed from a monomer containing nitrile groups and one diene.

Preferably the copolymer used is hydrogenated butadiene acrylonitrile.

According to the present invention the copolymer used is obtained frommonomers containing nitrile groups in a percentage of between 33 and 49%in weight with respect to the final copolymer.

Even more preferably the copolymer used is obtained from monomerscontaining nitrile groups in a percentage of 39% in weight with respectto the final copolymer, for example it is possible to use a mixtureconsisting of 50% THERBAN 3446 (Bayer registered trademark) and 50%THERBAN 4307 (Bayer registered trademark).

Advantageously the elastomer compound also comprises fibres, preferablyin a percentage in weight of between 0.5 and 15% with respect to theelastomeric material and preferably having a length of between 0.1 and10 mm.

The use of fibres maintains appropriate mechanical characteristics ofthe body compound and therefore helps to avoid occurrence of theabove-mentioned problems.

In addition to the main elastomer, the elastomeric compound can alsocontain other elastomers and furthermore conventional additives such as,for example, reinforcing agents, fillers, pigments, stearic acid,accelerators, vulcanisation agents, antioxidants, activators,initiators, plasticisers, waxes, prevulcanisation inhibitors andsimilar.

For example, as filler carbon black or white filler can be used, whichis generally added in a quantity of between 5 and 200 phr, preferablyapproximately 70 phr. Talc, calcium carbonate, silica and similar canalso be added in a quantity generally between 5 and 150 phr ordispersions in oil containing fillers. Organosilanes can also be used inquantities of between 0.1 and 20 phr. Sulphur donor vulcanisation agentscan be used, for example amino disulfides and polymeric polysulfides orfree sulphur or organic and non-organic peroxides. The quantity addedvaries according to the type of rubber and the type of vulcanisationagent adopted and is generally between 0.1 and 10 phr. Theantidegradation agents most commonly used in composition of the compoundare microcrystalline waxes, paraffin waxes, monophenols, bisphenols,thiophenols, polyphenols, derivatives of hydroquinones, phosphites,mixtures of phosphates, thioesters, naphthylamines, diphenol amines,derivatives of substituted and non-substituted diarylamines,diarylphenylendiamines, paraphenylendiamines, quinolines and mixtures ofamines. The antidegradation agents are generally used in quantities ofbetween 0.1 and 10 phr. Representatives of the process oils that can beused are dithiobisbenzanilide, polypara-dinitrosobenzene,xylilmercaptans, polyethlyene glycol, petroleum oils, vulcanisedvegetable oils, phenolic resins, synthetic oils, petroleum resins,polymeric esters. The process oils can be used in a conventionalquantity of between 0 and 140 phr. Among the initiators stearic acid isconventionally used in a quantity of between 1 and 4 phr.

Conventional additives can also be added such as calcium oxide, zincoxide and magnesium oxide, generally in a quantity of between 0.1 and 25phr. Conventional accelerators are also used or combinations ofaccelerators such as, for example, amines, disulphides, guanidine,thiourea, thiazoles, sulphydryl compounds, sulphenamides,dithiocarbamates and xanthates generally in quantities of between 0.1and 100 phr.

The fabric 5 coating the teeth 4 or the fabric 7 coating the back 6 canconsist of one or more layers and can, for example, be obtained by meansof the weaving technique known as 2×2 twill.

Fabrics 5,7 preferably consist of a polymeric material, preferablyaliphatic or aromatic polyamide, even more preferably polyamide 6/6 withhigh thermal resistance and toughness.

The fabrics 5,7 can also be advantageously of the type in which eachweave thread consists of an elastic thread as core and at least onecomposite thread wound on the elastic thread, where the composite threadcomprises a thread with high thermal and mechanical resistance and atleast one covering thread wound on the thread with high thermal andmechanical resistance.

A toothed belt 1 according to the present invention comprises aresistant layer 8 positioned on the outside of the fabric 5.

Preferably an adhesive 9 is also positioned between the fabric 5 and theresistant layer 8.

The resistant layer 8 consists of a fluorinated polymer plastic with theaddition of an elastomeric material; the fluorinated polymer plastic ispresent in a larger quantity in weight with respect to the elastomericmaterial.

An example of a resistant layer which can be used is described, forexample, in the patent EP 1 157 813 in the name of the same applicant.

According to the present invention the fluorinated plastomer ispreferably a compound based on polytetrafluoroethylene.

Preferably the elastomeric material with which the fluorinated polymerplastic is mixed to form the resistant layer 8 is HNBR, even morepreferably it is an HNBR modified with a zinc salt of polymethacrylicacid, for example ZEOFORTE ZSC (Nippon Zeon registered trademark) can beused.

Preferably an adhesive material can be placed between the coating fabric5 and the resistant layer 8.

Preferably, to ensure the necessary resistance, the resistant layer 8has a weight of between 150 and 400 g/m2, which is equivalent to anaverage thickness of between 0.050 and 1 mm.

Preferably the fluorinated polymer plastic is present in a quantity ofbetween 101 and 150 in weight for 100 parts of elastomeric material.

The resistant layer 8 furthermore comprises a peroxide as vulcanisationagent. The peroxide is normally added in a quantity of between 1 and 15parts in weight with respect to 100 parts of elastomeric material.

It has surprisingly been discovered that, for the compound constitutingthe body of the belt, the use of an elastomeric material with copolymerbase formed of one diene and one monomer containing nitrile groups in apercentage of between 33 and 49% in weight with respect to the finalcopolymer, in combination with the use of a resistant layer 8 above thelayer of fabric 5 coating the teeth 4 produced as previously described,eliminates the above-mentioned problems and, in particular, thereduction in mechanical characteristics, reduced adhesion, lessefficient meshing and less resistance to wear.

Preferably the resistant layer 8 is also placed over the fabric 7 thatcoats the back 6, when said fabric 7 is present.

In this case the resistant layer 8 prevents penetration of the oil alsofrom the side of the back 6 of the toothed belt 1 and is particularlyadvantageous when the toothed belt 1 is used in control systems in whichthe back 6 of the belt is in contact with sliding blocks or tighteners.In these systems, in fact, the oil remains between the contact surfaceof the sliding block or tightener with the belt and the back of thebelt, thus favouring penetration inside the compound constituting thebody.

Preferably the toothed belt 1 can be treated on all the outer surfacesand, in particular, on the sides 10 where the body compound is moreexposed to attack by the oil, with a rubber resistant to expansion, forexample ENDURLAST (Lord registered trademark).

The resistant inserts 3 for the toothed belts of the present inventionare made, for example, of high resistance fibreglass.

The resistant inserts are also treated with RFL and in particular withan RFL designed to prevent absorption.

Preferably the RFL used comprises a latex formed of a monomer containingnitrile groups and one diene, for example HNBR or hydrogenated butadieneacrylonitrile. Even more preferably the latex is obtained from monomerscontaining nitrile groups in a weight percentage with respect to thefinal copolymer similar to the elastomeric material used to form thebody of the toothed belt 1.

Experimentally it has been found that the use of resistant inserts madeof material comprising high modulus fibres, aramidic fibres, PBO orcarbon fibres or made of several materials such as, for example, carbonfibres together with fibreglass, when treated with an RFL comprising anoil-resistant material, helps to avoid the problems underlying thepresent invention.

The toothed belt 1 is vulcanised according to common known methods whichare therefore not described in detail.

The belt 1 according to the present invention can be used, for example,in a timing control system for a motor vehicle of the type shown in FIG.2. The timing control system is shown in the figure as a whole by number11 and comprises a drive pulley 12 rigidly fixed to the drive shaft, notillustrated, a first 13 a and a second 13 b driven pulley and atightener 14 for tensioning the toothed belt.

According to a second alternative embodiment, illustrated in FIG. 3,number 20 refers to a toothed belt according to the present invention,which is provided with teeth on both faces and therefore features aresistant fabric that coats both sets of teeth.

A toothed belt 20 can, for example, be used in a timing control systemfor a motor vehicle of the type shown in FIG. 3. The timing controlsystem is shown in the figure as a whole by number 21 and comprises adrive pulley 22 rigidly fixed to the drive shaft, not illustrated, afirst 23 a, a second 23 b and a third 24 driven pulley.

According to a third embodiment of the present invention, illustrated inFIG. 4, a toothed belt 30 according to the present invention canadvantageously be used in a timing control system shown in the figure asa whole by number 31, which comprises a drive pulley 32 rigidly fixed tothe drive shaft, not illustrated, a first 33 a and a second 33 b drivenpulley, a sliding block tightener 34 and a sliding block 35.

In use, the toothed belts 1, 20 and 30 in the respective control systems11,21 and 31 are in direct contact with oil.

The figures from 2 to 4 refer to control systems relating to themovement of balancing countershafts, but it is clear that the toothedbelt according to the present invention can also be used in so-called“cam to cam” or for movement of the oil pump. In these cases the belt ispartially immersed in an oil bath during operation.

Furthermore it is also possible to use the belt of the present inventionin the main transmission for movement of the cams and also for movementof the injection pump in diesel engines.

In particular, the belt according to the invention has undergoneduration tests in contact with oil. For the performance of these testsit was used on control systems comprising a drive pulley, a drivenpulley and a tightener in which oil is sprayed by means of a pipedirectly onto the belt.

The conditions in which the test was performed are shown in table 1.

TABLE 1 Belt type Dayco 122RPP + 150 Speed 6000 rpm Specific load 40N/mm Oil temperature 140° C. Oil quantity 22 1/h Number of drive pulleyteeth 22 Number of driven pulley teeth 44 Tightener diameter 47 mm

The toothed belts tested in these conditions resisted at least80,000,000 cycles.

From an examination of the characteristics of the toothed belt 1produced according to the present invention the advantages that can beobtained with it are evident.

It has been experimentally ascertained that the combination of use ofthe resistant layer 8 on the fabric 5 with the elastomeric material usedto form the body 2 of the toothed belt enables the toothed belts to passthe duration tests which they undergo for use in motor vehicles,therefore avoiding all the problems of the known toothed belts when usedin contact with oil, in particular reduction of the mechanicalcharacteristics, reduced adhesion, less efficient meshing and lessresistance to wear.

The toothed belt according to the present invention will now bedescribed also via non-restrictive examples.

Example 1

Table 2 shows the characteristics of a fluorinated polymer plastic whichcan be used in a resistant layer 8 according to the present invention.

TABLE 2 ZONYL MP 1500 Average density ASTM D 1457 350-400 g/l Meltingtemperature ASTM D 1457 325 +/− 10° C. Particle dimension distribution(Laser Average 6 μm Microtac) Specific surface area (NitrogenAbsorption) 11

Example 2

Table 3 shows the characteristics of an elastomeric material in aresistant layer 8 according to the present invention.

TABLE 3 ZETPOL 1010 Bonded acrylonitrile % in weight 44% Mooney unit MS1 + 4 ml 100° C. 78-92 Specific gravity 0.98 (g/cm³)

Example 3

Table 4 shows the chemical composition of a resistant layer 8 producedaccording to the present invention. Said resistant layer has a thicknessof 0.250 mm.

TABLE 4 Elastomeric material as per example 2 100 phrFluoropolymer-based additive as per example 125 phr 1 Peroxide  6 phr

1. An oil-resistant toothed belt comprising a body and a number of teethextending from at least one first surface of said body; said teeth beingcoated by a first fabric, said fabric being externally coated with aresistant layer, in which: said resistant layer comprises a fluorinatedplastomer, a first elastomeric material and a vulcanisation agent; saidfluorinated plastomer is present in said resistant layer in a largerquantity than said first elastomeric material; said body comprises acompound based on a second elastomeric material formed of a copolymerobtained from a dienic monomer and a monomer containing nitrile groups;said nitrile groups are in percentage between 33% and 49% in weight withrespect to the weight of said copolymer.
 2. The toothed belt accordingto claim 1, wherein it is suitable to resist for its lifetime when usedin direct contact or partially immersed in oil.
 3. The toothed beltaccording to claim 1, wherein said toothed belt is suitable to pass theduration tests which they undergo for use in motor vehicles.
 4. Thetoothed belt according to claim 1, wherein it resists at least80,000,000 cycles in the duration tests which they undergo for use inmotor vehicles.
 5. The toothed belt according to claim 1, wherein saidnitrile groups are in percentage 39% in weight.
 6. The toothed beltaccording to claim 1, wherein said second elastomeric material compriseshydrogenated butadiene acrylonitrile.
 7. The toothed belt according toclaim 6, wherein said hydrogenated butadiene acrylonitrile is modifiedwith a zinc salt of polymethacrylic acid.
 8. The toothed belt accordingto claim 1, wherein said resistant layer comprises said fluorinatedplastomer in a quantity in weight of between 101 and 150 parts in weightwith respect to said elastomeric material.
 9. The toothed belt accordingto claim 1, wherein said fluorinated plastomer ispolytetrafluoroethylene.
 10. The toothed belt according to claim 1,wherein the back of said belt is coated by a second fabric.
 11. Thetoothed belt according to claim 1, wherein said second fabric is coatedon the outside by a second resistant layer.
 12. The toothed beltaccording to claim 11, wherein said second resistant layer is equal tosaid first resistant layer.
 13. The toothed belt according to claim 1,wherein said elastomeric material comprises fibres.
 14. The toothed beltaccording to claim 13, wherein said fibres are present in a quantity inweight of between 0.5 and 15% with respect to said elastomeric material.15. The toothed belt according to claim 1, wherein it comprisesresistant inserts chosen from the group consisting of aramidic fibres,PBO and carbon fibres.
 16. The toothed belt according to claim 15,wherein said resistant inserts have been treated with an RFL comprisingan oil-resistant latex.
 17. The toothed belt according to claim 16,wherein said latex comprises an elastomeric material formed of acopolymer obtained from a dienic monomer and a monomer containingnitrile groups.
 18. The toothed belt according to claim 1, wherein itcomprises between the teeth and said back sides treated with a polymerresistant to expansion.
 19. Use in direct contact with oil or partiallyimmersed in oil of a fluorinated plastomer in a resistant layer of atoothed belt, said toothed belt comprising a body and a number of teethextending from at least one first surface of said body; said teeth beingcoated by a first fabric, said fabric being externally coated with saidresistant layer.
 20. A toothed belt for use with oil or in an oil wetenvironment comprising a body and a number of teeth extending from atleast one first surface of said body; said teeth being coated by saidfabric, said fabric being coated with a fluorinated plastomer.